Magnetic and structural properties of CaO–SiO2–P2O5–Na2O–Fe2O3 glass ceramics

Magnetic properties of glass ceramics derived from glasses with composition 41CaO·(52−x)SiO₂·4P₂O₅·xFe₂O₃·3Na₂O (2?x?10 mol% iron oxide (Fe₂O₃)) are reported. Structural investigation revealed the presence of nanocrystalline magnetite phase in the heat-treated samples containing x?2 mol% Fe₂O₃. Magnetic hysteresis cycles of the glass-ceramic samples were obtained with a maximum applied field of ±20 kOe as well as a low field of ±500 Oe, in order to evaluate the potential of these glass ceramics for hyperthermia treatment of cancer. Samples with x>2 mol% of iron oxide exhibited magnetic behavior similar to soft magnetic materials with low coercivity. The evolution of magnetic properties in these samples as a function of iron oxide molar concentration is correlated with the amount and crystallite size of magnetite phase present in them.     

Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

New germanosilicate glasses giving the crystallization of yttrium iron garnet Y₃Fe₅O₁₂ (YIG) and Bi-doped YIG, 23Na₂O-xBi₂O₃-(12−x)Y₂O₃-25Fe₂O₃-20SiO₂-20GeO₂ (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mössbauer effect measurements that iron ions in the glasses are present mainly as Fe³⁺. It is suggested from the X-ray diffraction analyses and magnetization measurements that Si⁴⁺ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32-60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO₄ fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe³⁺ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.     

EPR and magnetic susceptibility studies of iron ions in ZnO-Fe2O3-SiO2-CaO-P2O5-Na2O glasses

Room temperature electron paramagnetic resonance (EPR) spectra and temperature dependent magnetic susceptibility data have been obtained on bulk x(ZnO,Fe₂O₃)(65−x)SiO₂20(CaO, P₂O₅)15Na₂O (6≤x≤21 mole%) glasses prepared by melt quenching method. EPR spectra of the glasses revealed absorptions centered at g≈2.1 and 4.3. The variations of the intensity and line width of these absorption lines with composition have been interpreted in terms of the variation in the concentration of the Fe²⁺ and Fe³⁺ ions in the glass and the interaction between the iron ions. EPR and magnetic susceptibility data of the glasses reveal that both Fe²⁺ and Fe³⁺ ions are present in the glasses, with their relative concentration being dependent on the glass composition. The studies reveal superexchange type interactions in these glasses, which are strongly dependent on their iron content.     

Spectroscopic analysis and magnetic susceptibility of CuO-TeO2-V2O5 glasses

This article reports on the structure of the glassy system xCuO-65TeO₂-(35−x)V₂O₅, 5≤x≤10 mol% which was studied using infrared (IR) and Raman spectroscopy methods as well as magnetic susceptibility measurements. IR and Raman spectroscopy analysis reveals the presence of four main absorption bands attributed to [TeO₃], [TeO₄], [VO₄], and [VO₅] structure units. It suggests that Cu²⁺ ions occupy the available open spaces of the Te-O network without straining the bonds too much. Increasing the concentration of Cu²⁺ ions beyond 5 mol% results in the modification of the glass by straining and locally distorting the surrounding of the Te-O network. The magnetic susceptibility of these materials was investigated in the temperature range of 5-200 K revealing the paramagnetic behavior described by the Curie-Weiss law and indicating the presence of weak antiferromagnetic exchange interactions between Cu ions. The magnetic entropy change of the glasses was determined based on the temperature and magnetic field dependence of magnetization.     

Effect of iron doping on the characterization and transport properties of calcium phosphate glassy semiconductors

X-ray diffraction (XRD), differential scanning calorimeter (DSC), density (d) and dc conductivity (σ) of the glasses in Fe₂O₃-CaO-P₂O₅ system were reported. The dc conductivity in the temperature range 303-453 K was measured. The overall features of these XRD curves confirm the amorphous nature of the present samples. The density of glasses increases from 2.750 to 2.892 g/cm³ with increasing Fe₂O₃ content as a result of a strengthening of cross-linking within glass network. The glass temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The glasses had conductivities ranging from 10⁻⁹ to 10⁻⁵ Sm⁻¹ at temperatures from 303 to 453 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

Study of potassium-zinc borophosphate glasses

Potassium-zinc borophosphate glasses were prepared and studied in two compositional series xK₂O-(50−x)ZnO-10B₂O₃-40P₂O₅ and xK₂O-(50−x)ZnO-20B₂O₃-30P₂O₅ with x=0, 10, 20, 30, 40 and 50 mol% K₂O. The replacement of zinc by potassium decreases the density and increases the molar volume of these glasses, whereas glass transition temperature and chemical durability decrease with increasing potassium content. Structural changes were studied by ¹¹B and ³¹P MAS NMR and Raman spectroscopy. The observed changes in the spectra and the properties of the studied glasses can be ascribed to several reasons and namely to the differences in the space occupied by cations Zn²⁺ and 2K⁺, the differences in the electronegativity of zinc and potassium and a large difference in the field strength of Zn²⁺ and K⁺ cations and thus higher ionicity of K-O bonds in comparison with Zn-O bonds.     

Preparation and study of magnetic properties of silico phosphate glass and glass-ceramics having iron and zinc oxide

The magnetic properties of 25SiO₂–50CaO–15P₂O₅–(10−x)Fe₂O₃−xZnO (where x=0, 2, 5 mol%) glass and glass-ceramics have been studied. These glasses are prepared by melt quench technique and heat treated at 800 °C for 6 h. Electron Spectroscopy for Chemical Analysis (ESCA) revealed that the fraction of non-bridging oxygen decreases with the increase in zinc oxide content. Evolution of crystalline phases in glass-ceramics has been studied by X-ray diffraction (XRD). The microstructure as seen by scanning electron microscopy (SEM) exhibits formation of nanosize particles. Effect of controlled heat treatment on magnetic properties was studied by means of a Superconducting Quantum Interference Device (SQUID) magnetometer. Mössbauer spectroscopy at room temperature was also carried out to determine the state of iron ions in glasses and glass-ceramics. Isomer shift values of the glasses suggest that Fe³⁺ and Fe²⁺ are in tetrahedral coordination. The analysis of the glass without ZnO shows about 58 wt% of total iron ions is in the Fe³⁺ state. The samples on heat treatment show improved magnetic properties due to the formation of magnetic nanoparticles. Magnetic studies revealed the relaxation of magnetic particles and the increase in saturation magnetization with addition of 2 mol% ZnO. Increase in ZnO content results in decrease in the strength of dipolar interactions.     

In vitro evaluation of bioactivity of CaO-SiO2-P2O5-Na2O-Fe2O3 glasses

Glasses with compositions 41CaO(52 − x)SiO₂4P₂O₅·xFe₂O₃3Na₂O (2 ≤ x ≤ 10 mol.%) were prepared by melt quenching method. Bioactivity of the different glass compositions was studied in vitro by treating them with simulated body fluid (SBF). The glasses treated for various time periods in SBF were evaluated by examining apatite formation on their surface using grazing incidence X-ray diffraction, Fourier transform infrared reflection spectroscopy, scanning electron microscopy and energy dispersive spectroscopy techniques. Increase in bioactivity with increasing iron oxide content was observed. The results have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass composition.     

Study on the mechanisms of photoinduced carriers separation and recombination for Fe-TiO2 photocatalysts

The iron(III)-ion doped TiO₂ (Fe³⁺-TiO₂) with different doping Fe³⁺ content were prepared via a sol-gel method. The as-prepared Fe³⁺-TiO₂ nanoparticles were investigated by means of surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and the photoelectrochemical properties of Fe³⁺-TiO₂ catalysts with different Fe³⁺ content are performed by electrical impedance spectroscopy (EIS) as well as photocatalytic degradation of RhB are studied under illuminating. Based on the experiment results, the mechanism of photoinduced carriers separation and recombination of Fe³⁺-TiO₂ was revealed: that is, the Fe³⁺ captures the photoinduced electrons, inhibiting the recombination of photoinduced electron-hole pairs, this favors to the photocatalytic reaction at low doping concentration (Fe/Ti ≤ 0.03 mol%); while Fe³⁺ dopant content exceeds 0.03 mol%, Fe₂O₃ became the recombination centers of photoinduced electrons and holes because of that the interaction of Fe₂O₃ with TiO₂ leads to that the photoinduced electrons and holes of TiO₂ transfer to Fe₂O₃ and recombine quickly, which is unfavorable to the photocatalytic reaction.     

Structural and optical properties of lithium borobismuthate glasses

Glasses with compositions 25Li₂O-(75−x)Bi₂O₃-x B₂O₃, with 0?x?30 mol%, have been prepared using the melt quenching technique. The density and the molar volume have been determined. IR spectroscopy is used as a structural probe of the nearest neighbor environment in the glass network. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400-1100 nm. The values of the optical band gap E_g^opt for indirect transition and refractive index have been determined for 0?x?30 mol%. The average electronic polarizability of the oxide ion α_o²⁻ and the optical basicity have been estimated from the calculated values of the refractive indices. Variations in the different physical parameters such as the density, molar volume, optical band gap, refractive index, average electronic polarizability of the oxide ion and optical basicity with B₂O₃ content have been analyzed and discussed in terms of the changes in the glass structure.     

Hydrothermal synthesis and structural characterization of (1−x)α-Fe2O3-xSnO2 nanoparticles

Structural and morphological characteristics of (1−x)α-Fe₂O₃-xSnO₂ (x=0.0-1.0) nanoparticles obtained under hydrothermal conditions have been investigated by X-ray diffraction (XRD), transmission Mössbauer spectroscopy, scanning and transmission electron microscopy as well as energy dispersive X-ray analysis. On the basis of the Rietveld structure refinements of the XRD spectra at low tin concentrations, it was found that Sn⁴⁺ ions partially substitute for Fe³⁺ at the octahedral sites and also occupy the interstitial octahedral sites which are vacant in α-Fe₂O₃ corundum structure. A phase separation of α-Fe₂O₃ and SnO₂ was observed for x≥0.4: the α-Fe₂O₃ structure containing tin decreases simultaneously with the increase of the SnO₂ phase containing substitutional iron ions. The mean particle dimension decreases from 70 to 6 nm, as the molar fraction x increases up to x=1.0. The estimated solubility limits in the nanoparticle system (1−x)α-Fe₂O₃-xSnO₂ synthesized under hydrothermal conditions are: x≤0.2 for Sn⁴⁺ in α-Fe₂O₃ and x≥0.7 for Fe³⁺ in SnO₂.     

Effect of Bi2O3 on EPR, optical transmission and DC conductivity of vanadyl doped alkali bismuth borate glasses

Glasses with composition xBi₂O₃·(30−x)M₂O·70B₂O₃ (M=Li, Na) containing 2 mol% V₂O₅ have been prepared over the range 0≤x≤15 (x is in mol%). The electron paramagnetic resonance spectra of VO²⁺ of these glasses have been recorded in the X-band (≈9.3 GHz) at room temperature (RT≈300 K). Spin Hamiltonian parameters, g_∥, g_⊥, A_∥, A_⊥, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. The molecular orbital coefficients, α² and γ², have been calculated by recording the optical transmission spectra. In xBi₂O₃·(30−x)Li₂O·70B₂O₃ glasses there is decrease in the tetragonality of the V⁴⁺O₆ complex for x up to 6 mol% whereas for x≥6 mol%, tetragonality increases. In xBi₂O₃·(30−x)Na₂O·70B₂O₃ glasses there is increase in the tetragonality of the V⁴⁺O₆ complex with increasing x. The 3d_xy orbit expands with increase in Bi₂O₃:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported. The DC conductivity increases with increase in temperature. The order of conductivity is 10⁻⁵ ohm⁻¹ m⁻¹ at low temperature and 10⁻³ ohm⁻¹ m⁻¹ at high temperature. The DC conductivity decreases and the activation energy increases with increase in Bi₂O₃:M₂O ratio.     

Temperature-dependent Fe Mössbauer spectroscopy and local structure of the mullite-type Bi2(FexGa1−x)4O9 (0.1≤x≤1) solid solution

The Bi₂(Fe_xGa_1−x)₄O₉ oxide solid solution possessing a mullite-type structure has been investigated by ⁵⁷Fe Mössbauer spectroscopy in dependence of composition (0.1≤x≤1) and temperature (293≤T/K≤1073). The spectra have been fitted with two doublets for tetrahedrally and octahedrally coordinated high-spin Fe³⁺ ions, respectively. The experimental areas of the subspectra were used to determine the distribution of iron on the two inequivalent structural sites. The fraction of iron cations occupying the octahedral site is found to increase with decreasing Fe content and the cation distribution is almost independent of temperature. The unusual temperature dependence of the quadrupolar splitting, QS, observed for the octahedral site with dQS/dT>0 is discussed in connexion with structural data for Bi₂Fe₄O₉. The temperature dependence of Mössbauer isomer shifts and signal intensities is examined in the context of local vibrational properties of iron on the two inequivalent sites of the mullite-type lattice structure.     

Physical, optical, structural and gamma-ray shielding properties of lead sodium borate glasses

Lead sodium borate glasses with compositions xPbO:20Na₂O:(80−x)B₂O₃ (where x=5, 10, 15, 20, 25, 30, 35, 40, 45, 50 and 55 mol%) have been prepared using melt-quenching method and investigated on their optical, physical, structural and gamma-rays shielding properties. The densities of these glass samples were increased with increase in PbO concentration. The FTIR spectra and molar volumes indicate that PbO acts differently on this glass structures over their compositions. For the PbO composition less than 20 mol%, Pb²⁺ is incorporated as network former, while it acts as network modifier for the composition from 20-55 mol%. For gamma-ray shielding properties, parameters such as mass attenuation coefficients, effective atomic number and half value layer were increased with increase in PbO concentration. Our results showed relative difference between theory and experiment of less than 1% between experimental and theoretical values. Moreover half value layers of the glass systems have been compared with some standard radiation shielding materials and they exhibited better shielding properties than barite concrete and ferrite concrete at 15 and 25 mol% of PbO, respectively.     

Optical,physical and structural studies of vanadium doped P2O5–BaO–Li2O glasses

Glasses in the compositions (Li₂O)₂₅–(BaO)₂₅–(P₂O₅)_50−x–(V₂O₅)_x (with x=0.5,1.0,1.5,2.0,2.5, and 3.0 mol%) have been prepared by the conventional melt quenching technique. X-ray powder diffractrogram show broad peaks which conforms glassy nature of the sample. Differential scanning calorimetry (DSC) thermograms show characteristic glass transition temperature (T_g) and it increases with increasing substitution of V₂O₅ for P₂O₅. The measured physical parameters like density, refractive index, ionic concentration and electronic polarizability are found to vary linearly with increasing x. Infrared spectra exhibits few bands, which are attributed to (P=O)_AS, (P=O)_S, (V=O), (P–O–P)_AS,P–O–V, (P–O–P)_AS and O–P–O vibrations. The optical absorption spectra of VO²⁺ ions in these glasses show three bands and are assigned to the ²B₂→ ²E,²B₂→ ²B₁ and ²B₂→ ²A₁ transitions. Electron paramagnetic resonance spectra of all the glass samples exhibit resonance signals characteristic of VO²⁺ ions. The values of Spin-Hamiltonian parameters indicate that the VO²⁺ ions are present in octahedral sites with tetragonal compression and belong to C_4V symmetry.     

Influence of frequency, temperature and composition on electrical properties of polycrystalline Co0.5CdxFe2.5−xO4 ferrites

Polycrystalline ferrites with general formula Co_0.5Cd_xFe_2.5−xO₄ (0.0?x?0.5) were prepared by sol-gel method. The dielectric properties ε′, ε″, loss tangent tan δ and ac conductivity σ_ac have been studied as a function of frequency, temperature and composition. The experimental results indicate that ε′, ε″, tan δ and σ_ac decrease as the frequency increases; whereas they increase as the temperature increases. These parameters are found to increase by increasing the concentration of Cd content up to x=0.2, after which they start to decrease with further increase in concentration of Cd ion. The dielectric properties and ac conductivity in studied samples have been explained on the basis of space charge polarization according to Maxwell and Wagner's two-layer model and the hoping between adjacent Fe²⁺ and Fe³⁺ as well as the hole hopping between Co³⁺and Co²⁺ ions at B-sites. The values of activation energies E_f for conduction process are determined from Arrhenius plots, and the variations in these activation energies as a function of Cd content are discussed. The complex impedance analysis is used to separate the grain and grain boundary of the system Co_0.5Cd_xFe_2.5−xO₄. The variations of both grain boundary and grain resistances with temperature and composition are evaluated in the frequency range 42 Hz-5 MHz.     

Investigation of spectroscopic properties and thermal stability of Er/Yb-co-doped Bi2O3-B2O3-Ga2O3 glasses

A series of Er³⁺/Yb³⁺-co-doped 60Bi₂O₃-(40−x) B₂O₃ -xGa₂O₃ (BBGA x=0, 4, 8, 12, 16 mol%) glasses have been prepared. The absorption spectra, emission spectra, fluorescence lifetime of Er³⁺:⁴I_13/2 level and thermal stability were measured and investigated. Three Judd-Ofelt intensity parameters Ω_t (t=2,4,6) (Ω₂=(4.67-5.93)×10⁻²⁰ cm², Ω₄=(1.50-1.81)×10⁻²⁰ cm², Ω₆=(0.92-1.17)×10⁻²⁰ cm²) of Er³⁺ ions were calculated by Judd-Ofelt theory. It is found that the Ω₆ first increases with the increase of Ga₂O₃ content from 0 to 8 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section () of Er³⁺: ⁴I_13/2→⁴I_15/2 transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=69-76 nm) of the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ions were measured. The results indicate that these new BBGA glasses can be used as a candidate host material for potential broadband optical amplifiers.     

Structural,optical and dielectric properties of Ni substituted NdFeO3

Present study reports the structural, optical and dielectric properties of Ni substituted NdFe_1−xNi_xO₃ (0 ≤ x ≤ 0.5) compounds prepared through the ceramic method. X-ray diffraction (XRD) confirmed an orthorhombic crystal structure of all the samples. Both unit cell volume and grain size were found to decrease with an increase in Ni concentration. Morphological study by Scanning electron microscope (SEM) shows less porosity with Ni substitution in present system. From UV–vis spectroscopy, the optical band gap was found to increase with Ni doping. This observed behavior was explained on the basis of reduction in crystallite size, unit cell volume and its impact on the crystal field potential of the system after Ni substitution. The dielectric properties (?′ and tanδ) as a function of frequency or temperature, and the ac electrical conductivity (σ_ac) as a function of frequency have been studied. Hopping of charge carriers between Fe²⁺ → Fe³⁺ ions and Ni²⁺ → Ni³⁺ ions are held responsible for both electrical and dielectric dispersion in the system. Wide optical band gap and a very high dielectric constant of these materials promote them to be a suitable candidate for memory based devices in electronic industry.     

Optical and electronic polarizability investigation of Nd-doped soda-lime silicate glasses

This paper reports on different physical and optical properties of Nd³⁺-doped soda-lime silicate glass. The glasses containing Nd³⁺ in (65−x)SiO₂:25Na₂O:10CaO:xNd₂O₃ (where x=0.0-5.0 mol%) have been prepared by the melt-quenching method. In order to understand the role of Nd₂O₃ in these glasses the density, molar volume, refractive index and optical absorption were investigated. The results show that the density and molar volume of the glasses increase with an increase in Nd₂O₃ concentration and consequently generate more non-bridging oxygen (NBOs) into glass matrix. The optical absorption spectra were measured in the wavelength range from 300 to 700 nm and the optical band gaps were determined. It was found that the optical band gap decreases with an increase in Nd₂O₃ concentration. On the basis of the measured values of density and refractive index, the Nd³⁺ ion concentration in glasses, the polarizability of oxide ions and optical basicity were theoretically determined.     

Effects of SrO/ZnO on structure and properties of UV-transmitting borophosphosilicate glass

UV-transmitting borophosphosilicate glasses series, 2Al₂O₃−xSrO-(18−x)ZnO-33.3P₂O₅-16.7B₂O₃-30SiO₂ glasses with x=0-18 mol% were prepared and studied. The substitution of SrO for ZnO increases the density and the thermal expansion coefficient (α), but decreases the molar volume (V_m). The glass transition temperatures (T_g) and softening points (T_d) vary within a small range. The relative chemical durability was determined by measuring the weight loss of a polished glass sample after immersion in deionized water at 50 °C for 24 h, the chemical durability of the glasses increases when x≤9, and drops when x>9. With the increasing SrO content, the UV transmittance of the glasses decreases mildly. The compositional dependence of E_opt shows a decrease trend with increasing SrO content. The structural changes with the glass compositions were examined by FT-IR and Raman spectra.